1. Field of the Invention
The present invention relates to systems and methods for coordinated control of a switched power capacitor with an integrated resonance protection system. More specifically, the invention relates to adjusting calculations made by the primary control system in response to a determination of a harmonic resonance condition by the resonance protection system.
2. Description of the Prior Art
Existing switched power capacitor control systems may include a primary control system and a harmonic resonance protection system. The primary control system determines if a capacitor switching operation is needed by comparing actual control parameters to target control parameters and determining if a switching operation would make the actual control parameters closer in value to the target control parameters. Target control parameters are predetermined. Actual control parameters are calculated by the primary control system based on measurements of voltages and currents obtained with voltage and current transformers respectively. If a switching operation is required, the primary control system further determines which capacitor bank is to be switched based on other factors such as, for example, a capacitor""s size and whether a capacitor is connected or disconnected.
The resonance protection system monitors the circuit for harmonic resonance conditions. Harmonic resonance conditions may be due to capacitor switching operations or system changes such as, for example, a load change, a system source impedance change, or a network topology change. Harmonic resonance may cause significant harmonic distortion in the system voltages and currents, which may increase the losses in the circuit and cause damage to equipment operating in the system due to overheating and vibration. When a resonance condition due to capacitor switching operation is detected, the protection system performs additional capacitor switching operation to de-tune the circuit from the sustained resonance. If a switching operation is required, the harmonic resonance protection system further determines which capacitor is to be switched based on other factors such as, for example, a capacitor""s size and whether a capacitor is connected or disconnected.
Existing switched power capacitor control systems may contain both an independent primary control system and an independent resonance protection system. The independence of these two systems results in several drawbacks. First, the independent systems must duplicate certain functions such as, for example, determining whether a capacitor is connected and generating a signal to control a capacitor. Second, the independent systems may, under certain circumstances, force the capacitor banks into a constant on/off operation deadlock. For example, the primary control system may determine that a certain capacitor bank needs to be switched on. If switching on this capacitor bank tunes the circuit to a resonance condition, then the resonance protection system will perform additional capacitor switching operations to de-tune the circuit from the sustained resonance. It is possible that the resonance protection system may determine to switch off the same capacitor bank that the primary control system switched on. Once the capacitor bank is switched off by the resonance protection system, the primary control system will switch the capacitor bank back on. This operation deadlock can cause excessive wear to the capacitors and the switching apparatus. Thus, it would be a great improvement in the art to integrate and coordinate the primary control system and the resonance protection system to avoid duplication of functions and switching deadlock.
The present invention is directed to systems and methods for coordinated control of a switched power capacitor with an integrated resonance protection function. The coordination system receives control parameters calculated by the primary control unit. The coordination system also receives from the resonance protection system an input indicating whether a harmonic resonance condition is present. If a harmonic resonance condition is present, the coordination system adjusts the control parameters. If no harmonic resonance condition is present, the control parameters calculated by the primary control system are not changed. The coordination system then performs capacitor bank switching operations based on either the control parameters originally calculated by the primary control system or the adjusted control parameters.